Season of Colours

Hands down, autumn is my favourite season. 

The colours. 

The warm days. 

The golden light. 

Maybe not so much the thought that winter is just around the corner, but everything else about autumn is a winner.

On a recent walk, I wondered how and why deciduous tress change colour but evergreen trees don't? And thanks to google, here's what I found out.

I learnt that red, yellow, gold and orange colours are actually in the leaves all the time. However they can't be seen because of all the chlorophyll in the leaves. Chlorophyll is a green pigment that's in all green plants and is responsible for absorbing light from the sun to provide energy for photosynthesis.

So what is photosynthesis? Well plants use a process called photosynthesis to make food. During photosynthesis plants trap light energy from the sun in their leaves. Plants use this energy from the sun to change water (which they get through air and soil) and carbon dioxide (from the air) into sugar called glucose. Glucose is used by plants for energy to make other substances like cellulose and starch.

Basically, photosynthesis is a function that converts solar energy into chemical energy. The chemical energy is stored for later use. A byproduct of photosynthesis is oxygen, which gets released into the air.

Three factors can limit the speed of photosynthesis ... the intensity of light, the carbon dioxide concentration and temperature.

During autumn because of the changes in the length of daylight and the change in temperature the leaves stop their food making process (photosynthesis). The chlorophyll breaks down and the green colour disappears which makes the yellows, oranges, golds and reds become visible.

Evergreen trees can keep their leaves/needles during winter because their foliage is coated in a waxy substance (cutin) which acts as a barrier and supports the leaves to retain water. Also they have cells which contain an anti-freeze chemical that adds further protection during winter. Water retention in the leaves and the anti-freeze component enable the leaves to carry on photosynthesising to continue providing the tree with energy, even in cold climates.

The reason leaves fall to the ground after their colourful display is because photosynthesising is no longer happening. Without food the stems of the leaves weaken, which causes them to fall.

And that's autumn in a nutshell.